bpf: Mark kfuncs as __noclone

Some distributions (e.g., CachyOS) support building the kernel with -O3,
but doing so may break kfuncs, resulting in their symbols not being
properly exported.

In fact, with gcc -O3, some kfuncs may be optimized away despite being
annotated as noinline. This happens because gcc can still clone the
function during IPA optimizations, e.g., by duplicating or inlining it
into callers, and then dropping the standalone symbol. This breaks BTF
ID resolution since resolve_btfids relies on the presence of a global
symbol for each kfunc.

Currently, this is not an issue for upstream, because we don't allow
building the kernel with -O3, but it may be safer to address it anyway,
to prevent potential issues in the future if compilers become more
aggressive with optimizations.

Therefore, add __noclone to __bpf_kfunc to ensure kfuncs are never
cloned and remain distinct, globally visible symbols, regardless of
the optimization level.

Fixes: 57e7c169cd6af ("bpf: Add __bpf_kfunc tag for marking kernel functions as kfuncs")
Acked-by: David Vernet <void@manifault.com>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Link: https://lore.kernel.org/r/20250924081426.156934-1-arighi@nvidia.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/include/linux/btf.h b/include/linux/btf.h
index 9eda6b113f9b4836c759eb7cd50b534231251710..f06976ffb63f9482f5794640a8c361da8854e5c6 100644 (file)
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -86,7 +86,7 @@
  * as to avoid issues such as the compiler inlining or eliding either a static
  * kfunc, or a global kfunc in an LTO build.
  */
-#define __bpf_kfunc __used __retain noinline
+#define __bpf_kfunc __used __retain __noclone noinline
 
 #define __bpf_kfunc_start_defs()                                              \
        __diag_push();                                                         \